8. HardRock 100-
Source: Iconosquare
Silverton, Colorado–Taking place in July every year this race goes through the mountains of Colorado featuring a few different extreme changes in altitude. The race is slightly over 100 miles, and the mountainous nature of the race challenges racers to have some kind of survivalist knowledge of the great outdoors. You need to finish the entire race within 48 hours, because you aren’t even supposed to stop at night. Runners commonly run at night with a headlamp to see ahead of their feet.